According to spec, we should wait animation frame callbacks before
taking (element) screenshot. As "element screenshot" would automatically
scroll into view, this solves intermittency.
Testing: Manually tested on pages, and
`take_element_screenshot/scroll_into_view.py` passes stably now.
Fixes: #39306
---------
Signed-off-by: Euclid Ye <yezhizhenjiakang@gmail.com>
This change removes the `DebugOption` (`-Z`) for touch event simulation
and moves the implementation of the feature to servoshell. The resaoning
for this is:
- This is really a servoshell feature and can be implemented on top of
the API. This moves more code out of the already too-complicated
renderer.
- I would like to consolidate `DebugOptions` into a `ServoLogOptions`
to collect all options for configuring Servo logging. This requires
moving away all of the non-logging options.
- Eventually touch event simulation will be able to reuse the fling
implementation from servoshell as we are actually simulating touch
events sent to the `WebView`.
Testing: This changes a conditional feature that's used for manual
debugging.
It is difficult to write tests for this as there are no servoshell tests
that
verify input handling.
Signed-off-by: Martin Robinson <mrobinson@igalia.com>
This should be the final PR for the Hash Function series that is
trivial.
Of note: I decided to transform `HashMapTracedValues<Atom,..>` to use
FxBuildHasher. This is likely not going to improve performance as Atom's
already have a unique u32 that is used as the Hash but it safes a few
bytes for the RandomState that is normally in the HashMap.
Signed-off-by: Narfinger <Narfinger@users.noreply.github.com>
Testing: Hash function changes should not change functionality, we
slightly decrease the size and unit tests still work.
Signed-off-by: Narfinger <Narfinger@users.noreply.github.com>
FNV is faster for hashing less than 16 bytes of data and the
cryptographic properties of the default HashMap are not needed for the
various ids.
Testing: This does not change functionality.
Signed-off-by: Narfinger <Narfinger@users.noreply.github.com>
Adds epoch to each WR image op command that is sent to compositor. The
renderer now has a `FrameDelayer` data structure that is responsible for
tracking when a frame is ready to be displayed. When asking canvases to
update their rendering, they are given an optional `Epoch` which denotes
the `Document`'s canvas epoch. When all image updates for that `Epoch`
are seen in the renderer, the frame can be displayed.
Testing: Existing WPT tests
Fixes: #35733
Signed-off-by: sagudev <16504129+sagudev@users.noreply.github.com>
Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Co-authored-by: Martin Robinson <mrobinson@igalia.com>
Forward any deserialization errors to the receiver, instead of panicking
on the router thread. This change was previously part of #38782, which
got reverted, since generic channels don't support custom router
callbacks yet. Propagating the error is still something we want, and
landing this separately will reduce the diff of the PR that introduces
generic callbacks.
Testing: Should be covered by existing tests. Also manually tested
https://github.com/servo/servo/issues/38939
---------
Signed-off-by: Jonathan Schwender <schwenderjonathan@gmail.com>
Signed-off-by: Jonathan Schwender <55576758+jschwe@users.noreply.github.com>
Co-authored-by: Martin Robinson <mrobinson@igalia.com>
Ports the channel returning the result of `GenerateFontKeys` to generic
channel
Testing: No functional changes - Covered by existing tests
Part of https://github.com/servo/servo/issues/38912
Signed-off-by: Jonathan Schwender <schwenderjonathan@gmail.com>
Instead of generating a frame for every display list, which might be one
rendered frame per `<iframe>`, generate only a single frame per call to
"update the rendering." This should make rendering more efficient when
there are `<iframe>`s present and also open up optimizations for
non-display list frames.
Testing: This could potentially reduce flashing of content during
rendering
updates, but that is very difficult to test.
Signed-off-by: Martin Robinson <mrobinson@igalia.com>
This reverts commit fb1c0a4c48.
Previously in `create_compositor_channel`, the [routing callback][1] was
setup so that a message received on the Compositor's IPC receiver will
be
forwarded to the local receiver using the `CompositorProxy` which also
takes care of waking up the event loop. In #38782, this was changed so
that the routing callbacks simply forwards the message directly without
going via the `CompositorProxy`. This breaks behaviours that rely on the
event loop being woken up on message sending, e.g. updating image frames
for animated gifs.
Since the GenericChannel API doesn't allow custom routing callbacks,
revert this change until we figure out a better solution.
[1]:
d2ccce6052/components/servo/lib.rs (L1114)
Signed-off-by: Mukilan Thiyagarajan <mukilan@igalia.com>
Signed-off-by: Mukilan Thiyagarajan <mukilan@igalia.com>
Adds a new memory report that aggregates the size of all scroll trees
from within all pipelines for each web view.
Testing: Acessing `about:memory`
Fixes: #38726
---------
Signed-off-by: criskell <96352451+criskell@users.noreply.github.com>
Besides migrating the channel to GenericChannel, this PR adds
`routed_channel_with_local_sender()` to `generic_channel`. This is for
existing use-cases, where we want to provide both an IPC capable
GenericSender, as well as a crossbeam Sender, for efficient sending if
the sender is in the same process.
Testing: All of our channels should send / receive at least some
messages during WPT tests.
Signed-off-by: Jonathan Schwender <schwenderjonathan@gmail.com>
This changes makes a variety of changes to ensure that the cursor is set
back to the default cursor when it leaves the `WebView`:
1. Display list updates can come after a mouse leaves the `WebView`, so
when refreshing the cursor after the update, base the updated cursor
on the last hovered location in the `DocumentEventHandler`, rather
than the compositor. This allows us to catch when the last hovered
position is `None` (ie the cursor has left the `WebView`).
2. When handling `MouseLeftViewport` events for the cursor leaving the
entire WebView, properly set the
MouseLeftViewport::focus_moving_to_another_iframe` on the input event
passed to the script thread.
3. When moving out of the `WebView` entirely, explicitly ask the
embedder to set the cursor back to the default.
Testing: This change adds a unit test verifying this behavior.
Fixes: #38710.
Signed-off-by: Martin Robinson <mrobinson@igalia.com>
This data structure is now unused after changes to the way that hit
testing works.
Testing: This is just removing dead code so no tests are necessary.
Signed-off-by: Martin Robinson <mrobinson@igalia.com>
The code was duplicated for handling in normal messages and handling
while shutting down messages.
This cleans it up and puts them into a function.
Testing: Does not change functionality.
Signed-off-by: Narfinger <Narfinger@users.noreply.github.com>
This change adds support for variable fonts via the
[`font-variation-settings`](https://developer.mozilla.org/en-US/docs/Web/CSS/font-variation-settings)
property.
There are three areas where we need to set the variation values:
* Webrender (`compositor.rs`), for drawing the glyphs
* Harfbuzz (`shaper.rs`), for most shaping tasks
* PlatformFont (`fonts/platform/`), for horizontal advances and kerning
For now, freetype is the only platform shaper that supports variable
fonts. I can't easily test the fonts with non-freetype shapers. Thats
why variable fonts are behind the `layout_variable_fonts_enabled` pref,
which is disabled by default.
<img width="1250" height="710" alt="image"
src="https://github.com/user-attachments/assets/1aee1407-f3a2-42f6-a106-af0443fcd588"
/>
<details><summary>HTML test file</summary>
```html
<style>
@font-face {
font-family: "Amstelvar VF";
src: url("https://mdn.github.io/shared-assets/fonts/variable-fonts/AmstelvarAlpha-VF.woff2")
format("woff2-variations");
font-weight: 300 900;
font-stretch: 35% 100%;
font-style: normal;
font-display: swap;
}
p {
font:
1.2em "Amstelvar VF",
Georgia,
serif;
font-size: 4rem;
margin: 1rem;
display: inline-block;
}
.p1 {
font-variation-settings: "wght" 300;
}
.p2 {
font-variation-settings: "wght" 625;
}
.p3 {
font-variation-settings: "wght" 900;
}
</style>
<div>
<p class="p1">Weight</p>
<span>(font-variation-settings: "wght" 300)</span>
</div>
<div>
<p class="p2">Weight</p>
<span>(font-variation-settings: "wght" 625)</span>
</div>
<div>
<p class="p3">Weight</p>
<span>(font-variation-settings: "wght" 900)</span>
</div>
</div>
```
</details>
https://github.com/user-attachments/assets/9e21101a-796a-49fe-b82c-8999d8fa9ee1
Testing: Needs decision on whether we want to enable the pref in CI
Works towards https://github.com/servo/servo/issues/37236
Depends on https://github.com/servo/stylo/pull/230
---------
Signed-off-by: Simon Wülker <simon.wuelker@arcor.de>
Instead of calculating this value in the compositor, calculate it in
`ScriptThread` now that it is straightforward to get this value from the
layout spatial tree. This allows removing some tricky callback code in
the Compositor.
Testing: This shouldn't change any observable behavior so is covered by
existing tests.
Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Instead of using WebRender hit testing to update the cursor, base it on
layout hit tests. This allows removing the majority of WebRender hit
test items and finally opens up the possibility of adding support for
custom cursors. In addition, this change fixes an issue where cursors
were not set properly on areas of the viewport that extended past the
page content.
Testing: This is difficult to test as verifying that the cursor changed
properly is beyond the capabilities of Servo's test harnesses.
Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Co-authored-by: Oriol Brufau <obrufau@igalia.com>
Before, the compositor was responsible for doing the hit testing during
input events within a page. This change moves that hit testing to
layout. With this change, epoch mismatches are no longer a bit deal and
we can simply ignore them, as the Constellation and Script will take
care of ignoring hit tests against scroll nodes and browsing contexts
that no longer exist. This means that hit testing retry support can be
removed.
Add the concept of a Script `HitTest` that transforms the coarse-grained
renderer hit test into one that hit tests against the actual layout
items.
Testing: Currently we do not have good tests for verifying the behavior
of
input events, but WebDriver tests should cover this.
Fixes: This is part of #37932.
Fixes: #26608.
Fixes: #25282.
Fixes: #38090.
Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Co-authored-by: Oriol Brufau <obrufau@igalia.com>
Co-authored-by: kongbai1996 <1782765876@qq.com>
Request a reflow when doing page zoom and only modify the scaling of the
WebView scene after the first root pipeline display list with the new
zoom is ready. In addition:
- store zoom limits in `Scale` types
- send `ViewportDetails` along with the display list so that we can
detect when the root pipeline scale is ready.
Testing: This is quite hard to test as it requires verification that
contents are zoomed appropriately at the right time.
Fixes: #38091.
Signed-off-by: Martin Robinson <mrobinson@igalia.com>
`WebDriverCommandMsg::TakeScreenshot` was the last thing blocking us
from removing constellation access in webdriver server. Now we can
happily remove it.
Surprisingly, this reduces binary size by 185KB for release profile in
Windows. #37737 removes a net total of 300 lines, but only reduced 98KB.
Testing: No regression after testing.
Signed-off-by: Euclid Ye <euclid.ye@huawei.com>
WPT tests are expected to create screenshots as soon as everything is
loaded. If an animation is happening adding the "reftest-wait" class to
the root element is appropriate way to delay the screenshot. Previously,
the
test harness was waiting for all animations to finish, but that is just
leading to many timeouts. Removing that code fixes the timeouts.
Two Servo-specific tests are also updated as they were written with
Servo's previous behavior in mind.
Testing: There are test result updates for this change. Many TIMEOUTS
now either correctly
PASS OR FAIL.
Fixes: #36931.
Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Similar to #37960, previously, `AvailHeight`, `AvailWidth`, `Height`,
`Width` ask compositor for screen metrics. This PR moves the request to
embedder.
This simplifies code, and reduces workload of compositor, which is
busier most of time.
Testing: No behaviour change. Updated some tests. `Width/Height` matches
other browsers.
---------
Signed-off-by: Euclid Ye <yezhizhenjiakang@gmail.com>
Previously, `screenX`, `screenY`, `outerHeight`, `outerWidth`, `moveBy`,
`resizeBy` ask compositor for window rectangle, which then return
"inner" rectangle after consulting Embedder.
This PR
1. removes `GetClientWindowRect` from compositor, and directly let
script ask embedder.
2. add `window_size` to `ScreenGeometry`
3. add a lot of docs to `ScreenGeometry`
Testing: `tests\wpt\mozilla\tests\mozilla\window_resizeTo.html` can now
pass for Headed Window.
Fixes: #37824
---------
Signed-off-by: Euclid Ye <yezhizhenjiakang@gmail.com>
Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Co-authored-by: Martin Robinson <mrobinson@igalia.com>
This creates a new method in shared/compositing/lib to generate image
keys that are send over the webview. This does not immediately return
the keys but goes over the constellation to receive the keys from the
IOCompositor. To make this more efficient, we now cache the keys in
image_cache in a simple FIFO order. The old blocking method stays intact
for now but got renamed to make the blocking clear.
The blocking calls that are left are in:
- `components/canvas/canvas_data.rs`
- `components/script/dom/htmlmediaelement.rs`
Testing: WPT tests should cover this as this doesn't change any
functionality.
Fixes: Was mentioned in
https://github.com/servo/servo/issues/37161#issuecomment-2915750051 and
part of https://github.com/servo/servo/issues/37086
---------
Signed-off-by: Narfinger <Narfinger@users.noreply.github.com>
Signed-off-by: gterzian <2792687+gterzian@users.noreply.github.com>
Co-authored-by: gterzian <2792687+gterzian@users.noreply.github.com>
Previously, our Servo-specific spatial tree scroll offsets were opposite
to
that of WebRender and also the web platform. This is due to the fact,
likely, that `winit` wheel directionality is also flipped. This change
has both the Servo spatial tree and the API take offsets that are
consistent with the web.
Any possible changes to the meaning of wheel directionality will be
handled in a followup change.
This is a breaking change to the Servo API.
Testing: This change updates unit tests.
Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Co-authored-by: Oriol Brufau <obrufau@igalia.com>
Before we only offered helper to add single image (no update or delete)
that got special IPC message, now we simplify this by offering all ops
helpers for dealing with single image (that happens most of the time),
that simply uses `update_images` under the hood. We also optimize for
this use case by using `SmallVec<[ImageUpdate; 1]>` to avoid alloc.
Testing: Just refactor, but code is covered by WPT tests
---------
Signed-off-by: sagudev <16504129+sagudev@users.noreply.github.com>
- Instead of eagerly computing `pageX` and `pageY`, collect the offset
from the content's initial containing block in the compositor and pass
that information through to `MouseEvent`. This prevents a layout flush
that was happening when eagerly trying to fetch `Document` scroll
offsets.
- Pass keyboard modifiers properly to `MouseEvent`.
- Now all this information is stored and passed as `Point2D` (typed) and
`Modifiers` which greatly reduces the amount of arguments that need to
be passed around.
Testing: It is difficult to test input events as they require WebDriver
which
isn't completely working yet. I have manually run Speedometer 2.1 and I
have
verified that this fixes the regression from #37601.
Fixes: #37601.
Signed-off-by: Martin Robinson <mrobinson@igalia.com>
The compositor always does the same thing with these events regardless
of the phase, so I think it is completely unecessary.
Testing: This shouldn't change behavior at all, so is covered by
existing tests.
Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Fix wheel event, either dispatched from window or webdriver:
- Positive deltaY means scrolling down, negative deltaY means scrolling
up
- Positive deltaX means scrolling right, negative deltaX means scrolling
left
Tests: Many scrolling interaction test will depend on this.
Signed-off-by: PotatoCP <kenzieradityatirtarahardja18@gmail.com>
Currently, the hover state will stay when the mouse moves out of the
webview, this PR fixes it
Testing: Hover on the `About` on servo.org, and then move the mouse up
to the browser UI, see the hover state resets
Signed-off-by: Tony <legendmastertony@gmail.com>
Previously, the Constellation would immediately ask the Compositor to
shut down a pipeline, even before the ScriptThread finished shutting it
down. This meant that the Compositor might remove a Pipeline and then
re-add it if the ScriptThread sent a Pipeline-related message (such as a
new display list) in the meantime.
This change makes it so that the Compositor waits for both the
Constellation and the ScriptThread to finish shutting down a Pipeline
before removing its data. In addition, the Constellation no longer
synchronously waits on the Compositor when shutting down Pipelines. This
was important when the Compositor would talk to the ScriptThread
directly, but isn't necessary any longer.
Testing: This is very hard to test, because it depends on the creation
and destruction of many iframes and the particular timing of of all
the messaging between Servo bits. That said, this was tested manually
by observing the completion of Speedometer 2.1.
Fixes: #37458.
Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Co-authored-by: Oriol Brufau <obrufau@igalia.com>
Revert "Remove duplication in dispatch_pending_point_input_events"
(https://github.com/servo/servo/pull/37426) which causes a serious bug.
Signed-off-by: batu_hoang <longvatrong111@gmail.com>
There are currently five places that scroll offsets are stored:
- DOM: A set of scroll offsets used for script.
- Layout: An array of scroll offsets that is used for tracking
layout-side scroll offsets.
- Layout: The scroll offsets stored in the `ScrollTree`. These are
currently unset and unused.
- Compositor: The scroll offsets stored in the `ScrollTree` mirrored
from layout.
- WebRender: The scrolled offsets stored in the WebRender spatial tree.
This change is the first step in combining the first three into the
layout `ScrollTree`. It eliminates the extra array of scroll offsets
stored in layout in favor of the storing them in the `ScrollTree`. A
followup change will eliminate the ones stored in the DOM.
- In addition the `ScrollState` data structure is eliminated as these
are
now stored in a `HashMap` everywhere when passing them via IPC.
- The offsests stored in layout can now never scroll past the boundaries
of the scrolled content.
Testing: This should not change behavior and is thus covered by existing
WPT tests.
Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Co-authored-by: stevennovaryo <steven.novaryo@gmail.com>
The compositor was accepting scroll offsets from the ScriptThread
without checking their boundaries. In some cases this could cause a
temporary discrepancy with the rendered scroll offset. This change makes
it so that all offset updates for scroll ayers in the compositor do not
scroll past the scroll boundaries of the node.
Testing: Two new tests pass with this change:
- `/css/css-position/sticky/position-sticky-left-003.html`
- `/css/css-position/sticky/position-sticky-top-003.html`
Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Instead of receiving message in the compositor during a spin of the
Servo event loop, receive them in libservo and then send them to the
compositor. This is preparation for allowing libservo to wait for
messages without spinning the main application event loop. This is
useful for two situations:
1. Allowing a blocking shutdown mode, which can be used to ensure clean
shutdown, regardless of how the API is used.
2. Allowing unit tests to wait until message are received instead of
using a timer like they do now.
Testing: This should not change behavior and is thus covered by existing
tests.
Fixes: This is part of #37371.
Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Implement action synchronization for wheel event. Previously only done
for pointer here https://github.com/servo/servo/pull/36932.
Testing:
`tests/wpt/meta/webdriver/tests/classic/perform_actions/wheel.py`
---------
Signed-off-by: PotatoCP <kenzieradityatirtarahardja18@gmail.com>
Follow up to [hit_test failed occasionally when the touch event is
sent](https://github.com/servo/servo/issues/35788#top) and
https://github.com/servo/servo/issues/36676#issuecomment-2882917136,
this PR adds a retry for hit tests with expired epoch in result.
Hit tests with outdated epoch mean it is too early to perform the hit
test.
Solution: retry hit test for the event on the next webrender frame.
The retry should guarantee that:
- Keep the correct order of events
- Retry time is not too long
Test cases: `./mach test-wpt --product servodriver -r
tests\wpt\tests\webdriver\tests\classic\element_click\events.py`
cc: @xiaochengh , @yezhizhen
---------
Signed-off-by: batu_hoang <longvatrong111@gmail.com>
This adds a *very* basic implementation of the `RefreshDriver` concept
to the Servo renderer. The initial idea is that controls the frequency
of display during animations. It eliminates the "slowdown" workaround
for WPT tests and now Servo animations don't move faster than 120 FPS
(observed to be slower in practice).
This establishes a base change which will be used to implement
non-display-list-producing layouts in a followup change.
Fixes#3406. (though much more work remains)
Testing: Covered by existing WPT tests.
Signed-off-by: Martin Robinson <mrobinson@igalia.com>
This change adds support for rendering static SVG images using the
`resvg` crate, allowing svg sources in the `img` tag and in CSS
`background` and `content` properties. There are some limitations in
using resvg:
1. There is no support for animations or interactivity as these would
require implementing the full DOM layer of SVG specification.
2. Only system fonts can be used for text rendering. There is some
mechanism to provide a custom font resolver to usvg, but that is not
explored in this change.
3. resvg's handling of certain edge cases involving lack of explicit
`width` and `height` on the root svg element deviates from what the
specification expects from browsers. For example, resvg uses the values
in `viewBox` to derive the missing width or height dimension, but
without scaling that dimension to preserve the aspect ratio. It also
doesn't allow overriding this behavior.
Demo screenshot:
<details>
<summary>Source</summary>
```
<style>
#svg1 {
border: 1px solid red;
}
#svg2 {
border: 1px solid red;
width: 300px;
}
#svg3 {
border: 1px solid red;
width: 300px;
height: 200px;
object-fit: contain;
}
#svg4 {
border: 1px solid red;
width: 300px;
height: 200px;
object-fit: cover;
}
#svg5 {
border: 1px solid red;
width: 300px;
height: 200px;
object-fit: fill;
}
#svg6 {
border: 1px solid red;
width: 300px;
height: 200px;
object-fit: none;
}
</style>
</head>
<body>
<div>
<img id="svg1" src="https://raw.githubusercontent.com/servo/servo/refs/heads/main/resources/servo.svg" alt="Servo logo">
</div>
<div>
<img id="svg2" src="https://raw.githubusercontent.com/servo/servo/refs/heads/main/resources/servo.svg" alt="Servo logo">
<img id="svg3" src="https://raw.githubusercontent.com/servo/servo/refs/heads/main/resources/servo.svg" alt="Servo logo">
<img id="svg4" src="https://raw.githubusercontent.com/servo/servo/refs/heads/main/resources/servo.svg" alt="Servo logo">
</div>
<div>
<img id="svg5" src="https://raw.githubusercontent.com/servo/servo/refs/heads/main/resources/servo.svg" alt="Servo logo">
<img id="svg6" src="https://raw.githubusercontent.com/servo/servo/refs/heads/main/resources/servo.svg" alt="Servo logo">
</div>
</body>
```
</details>
---------
Signed-off-by: Mukilan Thiyagarajan <mukilan@igalia.com>
Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Co-authored-by: Martin Robinson <mrobinson@igalia.com>
Implement missing synchronization in `dispatch_actions` of `WebDriver`.
https://w3c.github.io/webdriver/#dispatching-actions
> The user agent event loop has spun enough times to process the DOM
events generated by the last invocation of the >[dispatch tick
actions](https://w3c.github.io/webdriver/#dfn-dispatch-tick-actions)
steps.
- Add a way for `ScriptThread` to notify `WebDriver` about the
completion of input commands.
- Add a `webdriver_id` field for `InputEvent`. `ScriptThread` uses it to
distinguish WebDriver events and sends notification.
Tests:
`./mach test-wpt --product servodriver -r
tests\wpt\tests\webdriver\tests\classic\element_click\events.py` pass if
`hit_testing` pass. Check
[issue](https://github.com/servo/servo/issues/36676#issuecomment-2882917136)
cc: @xiaochengh
---------
Signed-off-by: batu_hoang <longvatrong111@gmail.com>
Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Co-authored-by: Martin Robinson <mrobinson@igalia.com>
This makes servo use less file descriptors for animated images and
avoids the crash described in
https://github.com/servo/servo/issues/36792.
Doing this also forces the end users to be more explicit about whether
they want to deal with all image frames or just the first one.
Previously, `Image::bytes` silently returned only the data for the first
frame. With this change there's now a `frames` method which returns an
iterator over all frames in the image.
Testing: No tests - this simply reduces the number of fds used. Servo
doesn't currently display animated gifs anyways.
Fixes: https://github.com/servo/servo/issues/36792
Signed-off-by: Simon Wülker <simon.wuelker@arcor.de>
When multiple WebViews are updating scroll events, instead of taking the
list of `WebView`s to avoid a double-borrow, batch scroll events into a
single transaction. This should make processing slightly more efficient
and avoids having to take the vector of WebViews.
Testing: No behavior change here and this aspect of WebView interaction
is untestable currently.
Signed-off-by: Martin Robinson <mrobinson@igalia.com>
